Optoelectronic modules include circuitry for converting between signal processing/transmission in an optical mode and signal processing/transmission in an electrical mode. The conversion may be in a single direction, but many modules provide bidirectional conversions to enable data exchanges in both modes. Optoelectronic modules are used in telecommunications central offices and in centralized computing facilities, where there is a significant demand for high bandwidth communications. As compared to metal interconnects, such as copper wiring, optical interconnects offer benefits with regard to both bandwidth and performance (e.g., less skew), while satisfying requirements relating to eye safety, electromagnetic compatibility, reliability, manufacturability, and cost.
It is common to couple an array of optoelectronic modules to a single substrate, such as a printed circuit board. Connectivity of a particular module is provided by coupling a module connector to a substrate connector. Edge-card style connectors are often used, but parallel optical links typically require the use of high-density electrical connectors to accommodate the larger number of electrical signals that must be managed. A single optical link may combine twelve optical channels that are separated into twelve electrical signals within the module. It follows that for each such link, there is a need for twelve electrical paths between the module and the substrate. Thus, the edge-card style connectors are sometimes replaced by connectors having pin-and-socket arrangements. The pins are rigid wire strands of electrically conductive material that are received within sockets having a fixed arrangement that corresponds to that of the pins.
A greater degree of flexibility with regard to the maintenance of the telecommunications central office or the centralized computing facility is available if the optoelectronic modules are replaceable. A difficulty is that the openings for inserting and removing optoelectronic modules through the housing of the host system typically allow the greatest degree of freedom for module movement in the Z axis, i.e., the axis that is parallel to the surface of the substrate on which the substrate connectors are mounted. This is shown in FIGS. 1 and 2. A printed circuit board 10 having an electrical connector 12 is shown as being within the interior of a housing that includes a bezel, or faceplate 14. The optoelectronic module 16 enters the housing through an opening within the faceplate, as indicated by the arrow 18 along the Z axis. However, the seating of the module must occur along the Y axis, which is represented by arrowed line 20. The module connector 22 must properly seat onto the substrate connector 12, but the direction of movement for seating the module is orthogonal to the greatest degree of freedom of module movement. Either before or after the module connector is seated, an optical fiber 29 is joined to the optoelectronic module to input/output optical signals.
One solution is to mount a substrate connector that has a seating direction perpendicular to the printed circuit board 10 (i.e., along the Z axis). The module connector 22 must be relocated to the rear surface of the optoelectronic module 16, rather than the bottom surface as shown in FIGS. 1 and 2. This allows the user to merely push the module rearwardly until the two connectors are seated together. This solution has benefits, but may impose restrictions on signal density. An alternative solution is described in U.S. Pat. No. 6,074,228 to Berg et al. Pressure contacts are preferably used for the connectors of Berg et al., rather than insertion contacts which require significantly more force in order to provide proper seating. The pressure contacts may be J-shaped leads which deflect slightly when press fit to contact pads of another connector. Since the required mating forces are reduced, the insertion force requirements are relaxed. The substrate connector of Berg et al. has a body that includes a guide member which is elongated along the Z axis. The elongated body of the substrate connector is surface mountable on a printed circuit board. The connector body also includes a camming element that is comprised of ramped regions. When the replaceable module is slid along the elongated body of the connector, a cam follower of the module raises and lowers the end of the module because of contact with the ramped regions of the camming element. While the raising and lowering of the module brings the module connector into contact with the leads of the substrate connector, the pressure contact may not be sufficient for some applications. Specifically, there may be concerns that less than all of the leads of the substrate connector have a low resistance connection to the contact pads of the module connector.